Fixtureless lensmeter and methods of operating same

ABSTRACT

A process is provided for determining characteristics of a lens, the process including obtaining a captured image of a pattern through a corrective lens; transforming the captured image to an ideal coordinate system; processing the captured image to determine an overall distortion from a reference pattern to the pattern of the captured image; determining a distortion of the captured pattern attributable to the corrective lens; and measuring at least one characteristic of the corrective lens. In some embodiments, the overall distortion is determined by detecting, in the captured image, at least one captured pattern landmark; determining a transformation from at least one ideal pattern landmark to the at least one captured pattern landmark; and determining for the corrective lens, from the transformation, a spherical power measurement, a cylinder power measurement, and an astigmatism angle measurement.

BACKGROUND Technical Field

The technical field generally relates to determining prescriptions ofcorrective lenses, and more particularly, in one aspect, to mobiledevice lensmeters and methods of operating such lensmeters.

Background Discussion

Eye doctors, eyeglass lens makers, and others who work with lenses oftenuse traditional lensmeters to determine the prescription (including thespherical power, cylinder power, and axis) of an unknown correctivelens. Such lensmeters typically involve shining a light source through apattern and a corrective lens mounted on a fixture of the lensmeter, andviewing the light at an eyepiece opposite the light source. Observingthe pattern's distorted appearance through the eyepiece, the distortioncan be correlated to a prescription known to create such a distortion.

A fixture holds the pattern, the corrective lens, and the eyepiece in anappropriate spacing and configuration to one another. Yet the fixture istypically large and heavy, making such an arrangement unwieldy andundesirable for use at home or in the field. Such traditional methods ofdetermining a prescription for a corrective lens also do not provide aconvenient way to convey the prescription information to others, such asan eye doctor or lens maker. While the information may be conveyed bytelephone, for example, the risk of transcription error or other issuesrises, making it less attractive for individuals to determine acorrective lens prescription in a convenient setting, such as home orwork. Those seeking to determine a prescription of an unknown correctivelens must therefore travel to an eye doctor or other professional, whichintroduces additional delays and costs to the process.

SUMMARY

According to one aspect, a process for determining characteristics of alens includes obtaining a captured image of a pattern through acorrective lens; transforming the captured image to an ideal coordinatesystem; processing the captured image to determine an overall distortionfrom a reference pattern to the pattern of the captured image;determining a distortion of the captured pattern attributable to thecorrective lens; and measuring at least one characteristic of thecorrective lens. According to one embodiment, the captured imageincludes a first region containing the pattern and created by lightpassing through the corrective lens, and a second region created bylight not passing through the corrective lens, and determining thedistortion of the captured pattern attributable to the corrective lensis performed at least in part with reference to the second region.According to a further embodiment, the pattern is a checkerboardpattern, and the second region contains a border. According to anotherembodiment, transforming the captured image to an ideal coordinatesystem includes detecting a plurality of captured reference landmarks inthe second region of the captured image; determining a transformationfrom a plurality of ideal reference landmarks to the plurality ofcaptured reference landmarks; and applying the transformation to thecaptured image.

According to another embodiment, the pattern is a first pattern and thecorrective lens is a first corrective lens, and obtaining the capturedimage of the pattern through the corrective lens includes obtaining acaptured image of the first pattern through the first corrective lensand a second pattern through the second lens.

According to yet another embodiment, processing the captured image todetermine the overall distortion from the reference pattern to thepattern of the captured image includes detecting, in the captured image,a plurality of captured pattern landmarks; determining a transformationfrom a plurality of ideal pattern landmarks to the plurality of capturedpattern landmarks; and determining for the corrective lens, from thetransformation, a spherical power measurement, a cylinder powermeasurement, and an astigmatism angle measurement. According to afurther embodiment, the transformation is a dioptric power matrix.

According to yet a further embodiment, obtaining the captured image ofthe at least one pattern through the corrective lens is performed at afirst location of a camera lens relative to the at least one pattern,further including capturing, at a second location of the camera lensrelative to the at least one pattern, a second captured image of the atleast one pattern through the corrective lens; detecting, in the secondcaptured image, the plurality of captured pattern landmarks; determininga second transformation from the plurality of ideal pattern landmarks tothe plurality of captured pattern landmarks; determining, for thecorrective lens, from the second transformation, the spherical powermeasurement, the cylinder power measurement, and the astigmatism anglemeasurement; and selecting a preferred transformation from the firsttransformation and the second transformation for which the sphericalpower measurement and the cylinder power measurement have a maximumabsolute value.

According to a still further embodiment, the captured image is capturedby a camera having a camera lens, and the corrective lens is positionedat a known location relative to the camera lens and the pattern.According to a further embodiment, determining the distortion of thecaptured image attributable to the corrective lens includes determininga distance between the camera lens and the pattern; and determining atleast one focal length of the corrective lens with reference to thedistance, the spherical power measurement, and the cylinder powermeasurement.

According to one embodiment, measuring the at least one characteristicof the corrective lens includes determining a prescription of thecorrective lens, the prescription including at least a sphere value, acylinder value, and an axis value. According to another embodiment,obtaining a captured image of a pattern through a corrective lensincludes obtaining, through a camera lens, a captured image of a firstpattern through a first corrective lens and a second pattern through asecond corrective lens, wherein the two patterns are spaced from eachother such that obtaining the captured image of the first patternthrough the first corrective lens and the second pattern through thesecond corrective lens can be performed when the first corrective lensand the second corrective lens are positioned at a known locationrelative to the camera lens and the first and second patterns.

According to yet another embodiment, the process further includesdetermining, from the captured image, a first location of a camera lensof a lensmeter through which the captured image was captured;identifying a direction to a second location relative to the firstlocation; guiding a user of the lensmeter to the second location; andcapturing a second captured image of the pattern through the correctivelens.

According to another aspect, a lensmeter includes a camera; a visualdisplay; and a processor coupled to the camera and configured to obtaina captured image of a pattern through a corrective lens; transform thecaptured image to an ideal coordinate system; process the captured imageto determine an overall distortion from a reference pattern to thepattern of the captured image; determine a distortion of the capturedpattern attributable to the corrective lens; and measure at least onecharacteristic of the corrective lens.

According to one embodiment, the captured image includes a first regioncontaining the pattern and created by light passing through thecorrective lens, and a second region created by light not passingthrough the corrective lens. According to a further embodiment, theprocessor is further configured to transform the captured image to anideal coordinate system by being configured to detect a plurality ofcaptured reference landmarks in the second region of the captured image;determine a transformation from a plurality of ideal reference landmarksto the plurality of captured reference landmarks; and apply thetransformation to the captured image. According

According to another embodiment, the processor is further configured toprocess the captured image to determine the overall distortion from thereference pattern to the pattern of the captured image by beingconfigured to detect, in the captured image, a plurality of capturedpattern landmarks; determine a transformation from a plurality of idealpattern landmarks to the plurality of captured pattern landmarks; anddetermine for the corrective lens, from the transformation, a sphericalpower measurement, a cylinder power measurement, and an astigmatismangle measurement. According to a further embodiment, the processor isfurther configured to obtain the captured image of the at least onepattern through the corrective lens at a first location, the processorfurther configured to capture, at a second location, a second capturedimage of the at least one pattern through the corrective lens; detect,in the second captured image, the plurality of captured patternlandmarks; determine a second transformation from the plurality of idealpattern landmarks to the plurality of captured pattern landmarks;determine, for the corrective lens, from the second transformation, thespherical power measurement, the cylinder power measurement, and theastigmatism angle measurement; and select a preferred transformationfrom the first transformation and the second transformation for whichthe spherical power measurement and the cylinder power measurement havea maximum absolute value. According to yet a further embodiment, thecaptured image is captured through a camera lens of the camera, and theprocessor is further configured to determine the distortion of thecaptured image attributable to the corrective lens by being configuredto determine a distance between the camera lens and the pattern; anddetermine at least one focal length of the corrective lens withreference to the distance, the spherical power measurement, and thecylinder power measurement.

According to one embodiment, the processor is further configured tomeasure the at least one characteristic of the corrective lens by beingconfigured to determine a prescription of the corrective lens, theprescription including at least a sphere value, a cylinder value, and anaxis value. According to another embodiment, the pattern is printed on aphysical medium. According to yet another embodiment, the pattern isdisplayed on an electronic display device.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments, and are intended to provide an overview or frameworkfor understanding the nature and character of the claimed subjectmatter. Particular references to examples and embodiments, such as “anembodiment,” “an example,” “one example,” “another embodiment,” “anotherexample.” “some embodiments,” “some examples,” “other embodiments,” “analternate embodiment,” “various embodiments,” “one embodiment,” “atleast one embodiments,” “this and other embodiments” or the like, arenot necessarily mutually exclusive and are intended to indicate that aparticular feature, structure, or characteristic described in connectionwith the embodiment or example and may be included in that embodiment orexample and other embodiments or examples. The appearances of such termsherein are not necessarily all referring to the same embodiment orexample.

Furthermore, in the event of inconsistent usages of terms between thisdocument and documents incorporated herein by reference, the term usagein the incorporated references is supplementary to that of thisdocument; for irreconcilable inconsistencies, the term usage in thisdocument controls. In addition, the accompanying drawings are includedto provide illustration and a further understanding of the variousaspects and embodiments, and are incorporated in and constitute a partof this specification. The drawings, together with the remainder of thespecification, serve to explain principles and operations of thedescribed and claimed aspects and embodiments.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are not limited to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. Embodiments of theinvention are capable of being practiced or of being carried out invarious ways. Also, the phraseology and terminology used herein is forthe purpose of description and should not be regarded as limiting. Theuse of “including,” “comprising,” or “having,” “containing,”“involving,” and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide an illustration anda further understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of any particular embodiment. Thedrawings, together with the remainder of the specification, serve toexplain principles and operations of the described and claimed aspectsand embodiments. In the figures, each identical or nearly identicalcomponent that is illustrated in various figures is represented by alike numeral. For purposes of clarity, not every component may belabeled in every figure. In the figures:

FIG. 1 is an illustration of a prior art lensmeter;

FIG. 2 is a block diagram of a lensmeter system according to one or moreembodiments;

FIG. 3 is a block diagram of a mobile device lensmeter according to oneor more embodiments;

FIG. 4 is a flow chart of a method for operating a mobile devicelensmeter according to one or more embodiments;

FIG. 5A is an illustration of a reference pattern group according to oneor more embodiments;

FIG. 5B is an illustration of a captured image of the reference patterngroup of FIG. 5A according to one or more embodiments;

FIG. 5C is the captured image of FIG. 5B after transformation to anideal coordinate system; and

FIG. 6 illustrates a number of pattern landmarks for a reference patterngroup and a pattern of a captured image according to one or moreembodiments.

DETAILED DESCRIPTION

According to one or more embodiments, the processes and systemsdisclosed allow a person to determine characteristics, such as aprescription, of one or more corrective lenses. In some embodiments, animage of one or more patterns is captured through the corrective lens bya camera device, and the distortion of the patterns is measured todetermine the characteristics of the corrective lens by a connectedcomputing device with specialized software. Embodiments discussed hereindescribe a lensmeter as a device configured to measure characteristicsof one or more corrective lenses without requiring the specific spacingand arrangement required by known lensmeters and enforced by thefixtures they incorporate. The present lensmeter may be a smartphone ortablet device on which specialized software (e.g., an app) is installedfor performing the claimed methods. Alternately, the lensmeter may havea fixed location (e.g., a camera embedded in a wall or fixture) that canmeasure characteristics of corrective lenses without requiring thecorrective lens and the pattern to be precisely spaced and arrangedrelative to the lensmeter. Such an arrangement may be suitable, forexample, in a retail environment, such as an optician location oreyeglass retailer.

The patterns may be displayed on a piece of paper, or may be displayedon a display of another device, such as a laptop computer. In someembodiments, the mobile device (i.e., the mobile lensmeter) and otherdevices (e.g., the other device displaying the pattern) may be paired,to allow the devices to communicate and interact during the measurementprocess. Examples herein depicting the mobile lensmeter as the mobiledevice itself are for illustrative purposes only, and it will beappreciated that functionality discussed herein with respect to the“mobile lensmeter” may be performed on, or in conjunction with, suchother devices as part of a mobile lensmeter system.

In some embodiments, two patterns are spaced and configured such thatthey are visible to the mobile lensmeter—each through one of a pair ofcorrective lenses in an eyeglass frame—when the corrective lenses arepositioned approximately halfway between the patterns and the lensmeterand oriented appropriately. Such an arrangement allows for easy,intuitive positioning of the mobile lensmeter, the patterns, and thecorrective lenses. Furthermore, the mobile lensmeter is configured todetermine the distance to the pattern and take that measurement intoaccount when determining the prescription. This design facilitates themanual positioning of the elements, eliminating the need for a fixture.In one embodiment, the pattern is a rectangle displayed on a physicalmedium or on a computer display. In some embodiments, the pattern issurrounded by a border having reference landmarks or other features usedto orient the captured image.

According to one or more embodiments, the disclosed processes andsystems transform the captured image to an ideal coordinate system tocompensate for the orientation of the lensmeter relative to the patternduring the image capture process. In some embodiments, thetransformation is made with reference to the location of referencelandmarks in the captured image relative to the location of referencelandmarks in a reference pattern group.

According to one or more embodiments, the disclosed processes andsystems process the captured image to determine an overall distortion bydetecting and determining the location of a number of captured patternlandmarks in the captured image. The system determines a transformationthat describes the distortion from the location of a number of referencepattern landmarks (in the ideal coordinate system) relative to thecorresponding captured pattern landmarks in the captured image. Anexpression of the transformation (e.g., a dioptric power matrix) may beused to determine measurements of the corrective lens, including aspherical power, a cylinder power, and an astigmatism angle. The portionof the overall distortion due to the corrective lens (as opposed to thelens of the lensmeter) may be determined in part by determining at leastone focal length of the corrective lens. Other characteristics of thecorrective lens may also be measured. The present embodiments are notlimited to sphero-cylindrical lenses, and may be suitable for lenseshaving other characteristics, such as single vision lenses, bifocallenses, trifocal lenses, progressive lenses, adjustable focus lenses, orlenses that correct for higher order aberrations.

According to one or more embodiments, multiple images may be capturedand analyzed to identify an image captured in a preferred orientation,e.g., where the corrective lens is closest to halfway between thelensmeter and the pattern.

According to one or more embodiments, a lensmeter is provided thatincludes a camera, a visual display, and a processor configured to carryout the processes described herein. The lensmeter may be a dedicatedlensmeter, or may be mobile device (e.g., a smartphone or a tabletdevice) executing lensmeter software, such as a downloadable app.

FIG. 1 illustrates a conventional optical lensmeter system 100 fordetermining a prescription and/or other unknown characteristics of acorrective lens 130. A light source 110 is directed through a pattern120 (e.g., a transparent target having a printed pattern with knowndimensions and arrangement) and the corrective lens 130 (and a number ofstandard and objective lenses, not shown) to an eyepiece 140. A viewerwhose eye is engaged with the eyepiece 140 can observe the way that thecorrective lens 130 distorts the light passing through the pattern 120.By measuring the distortive effect of the corrective lens 130, the usercan determine certain characteristics of the corrective lens 130,including the spherical power, cylindrical power, and axis measurementsof the corrective lens 130. The lensmeter system 100 requires a fixture150, including a lens holder 152, to maintain the pattern 130, thecorrective lens 130, and the eyepiece 140 in a precisely spaced andoriented arrangement. The optical principles underlying the operation ofthe lensmeter system 100 require that the specific spacing andorientation be maintained by the fixture 150.

Similarly, digital lensmeters can be used to image a pattern through asingle corrective lens, and use the distortion in the image to determinea prescription and/or other unknown characteristics of a correctivelens. Like conventional optical lensmeters, currently available digitallensmeters require a fixture for holding the corrective lens, thelensmeter lens, and the pattern in a precisely spaced and orientedarrangement.

FIG. 2 illustrates a block diagram of a lensmeter system 200 accordingto one or more embodiments. In the embodiments shown in FIG. 2, thesystem 200 includes a lensmeter 210, a corrective lens 220, and apattern 230. In operation, the lensmeter 210 captures an image of thepattern 230 through the corrective lens 220. The corrective lens 220distorts the light reflecting off the pattern 230 into the lensmeter210, and the distortive effect may be measured in order to determine oneor more unknown characteristics of the corrective lens 220, includingthe sphere, cylinder, and axis measurements.

The captured image of the pattern 230 is normalized by converting it toan ideal coordinate system using reference landmarks near the pattern230. The normalization compensates for rotation, tilt, or distancevariances in the spacing and orientation among the lensmeter 210, thecorrective lens 220, and the pattern 230. No fixture is thereforerequired in the lensmeter system 200. The normalized pattern 230 canthen be compared to a reference pattern, also in the ideal coordinatesystem, and the distortive effect of the corrective lens can be isolatedfrom the distortive effect of the lens of the lensmeter 210 itself.

In some embodiments, the pattern 230 is displayed on an electronicdisplay (not shown), such as a computer monitor, tablet or other mobiledevice, or the like, or is projected onto a surface by a projector. Forexample, the pattern 230 may be provided on a website accessible by thelensmeter system 200, or may be provided by or through a mobile apprunning on a mobile device. In other embodiments, the pattern 230 isprinted on a physical medium such as a piece of paper or plastic.

In some embodiments, two or more patterns may be used to allow fordetermining the characteristics of two or more corrective lensessimultaneously. In a preferred embodiment, two spaced patterns are used,with each pattern 230 being a rotation-variant checkerboard grid ofalternating black and white squares, where the number of rows in thecheckerboard differs from the number of columns by 1. Thisrotation-variant quality allows the lensmeter 210 to determine whetherthe pattern 230 is being viewed in a correct, upright position, oralternately is rotated on its side. In one embodiment, the pattern 230is a black-and-white checkerboard design having eight (8) rows and seven(7) columns. In another embodiment, the pattern 230 has 16 rows and 15columns. Other configurations or color combinations are also possible.

FIG. 3 is a block diagram of a lensmeter 210 according to someembodiments. In some embodiments, the lensmeter 210 is a consumer mobiledevice (e.g., a smartphone or tablet device) or computer (e.g., a laptopcomputer) running specialized software to perform the operationsdescribed herein. In other embodiments, the lensmeter 210 is a dedicatedlensmeter device. The lensmeter 210 includes a camera 310 having a lens312, and further includes a processor 320, a user interface 330, anetwork interface 340, a memory 350, and lensmeter software 360. In someembodiments, the camera 310 is an integral component of the lensmeter210. In other embodiments, the camera 310 may be an add-on component oraccessory. The processor 320 is coupled to the camera 310 and executessoftware 360 for the image capturing functions performed by thelensmeter 210. In some embodiments, the functionality of the lensmeter210 may be performed in conjunction with other devices as part of abroader lensmeter system. For example, in an embodiment wherefunctionality of the lensmeter 210 is performed by a user's smartphone,the smartphone may be paired with the user's laptop computer in order tocontrol the display of the patterns. In that example, the lensmeter 210may be considered to include both the user's smartphone and the laptopcomputer.

The user interface 330 receives input from, and provides output to, auser of the lensmeter 210. In some embodiments, the user interface 330displays to the user the image currently visible through the lens 312 ofthe camera 310, allowing the user to adjust the position or orientationof the lensmeter 210. In some embodiments, the user interface 330provides the user with a physical or on-screen button to interact within order to capture an image. In other embodiments, the image iscaptured automatically when the pattern 230 is detected in the image andcertain alignment, size, lighting, and resolution conditions are met.

The user interface 330 may also provide indications to the user to moveany of the lensmeter 210, the corrective lens 220, and the pattern 230to a different absolute position or orientation, or to a differentposition or orientation relative to each other. For example, the userinterface 330 may provide directions such as “MOVE FORWARD,” “MOVEBACKWARD.” “TILT LENSMETER FORWARD,” instructions conveyed with graphicsand illustrations, or other such directions, until the user haspositioned the lensmeter 210 such that the corrective lens 220 ispositioned at an optimal, known position relative to the lensmeter 210and the pattern 230; and until the lensmeter 210, the corrective lens220, and the pattern 230 are aligned so that the pattern 230 is viewablethrough the corrective lens 220 at the lensmeter 210. In someembodiments, the user interface 330 and/or other components of thelensmeter 210 may provide such instructions audibly, such as by recordedvoice instructions, or by an audible tone emitted at a frequencyproportional (or inversely proportional) to the distance of thelensmeter 210 from the correct position. In other embodiments, the userinterface 330 may provide an indication to the user once the user hascorrectly positioned the lensmeter 210, the corrective lens 220, and thepattern 230, for example by displaying a “green light” or thumbs-upicon. The user interface 330 may also allow a user to interact withother systems or components, such as by giving an instruction totransmit corrective lens prescription information to the user's doctor.

In some embodiments, the network interface 340 allows for access todownloads and upgrades of the software 360. In some embodiments, one ormore steps of the process described below may be performed on a server(not shown) or other component distinct from the lensmeter 210, and datamay be passed between the lensmeter 210 and the server via the networkinterface 340. The network interface 340 may further allow forautomatically uploading lens characteristics or prescription informationto another entity, e.g., the user's optometrist or another correctivelens provider.

Some or all of the processes described herein, as well as otherfunctions, may be performed by the lensmeter software 360 executing onthe lensmeter 210, or by other systems in communication with thelensmeter 210 (e.g., via the network interface 340).

FIG. 4 is a flow chart of a process 400 for determining characteristicsof a corrective lens according to one or more embodiments. Suchembodiments may be implemented using a system such as that shown inFIGS. 2 and 3.

The process begins at step 410.

At step 420, a captured image of a pattern is obtained through acorrective lens. The image is captured by a camera (e.g., camera 310).In some embodiments, the camera is part of, or attached to, a dedicatedlensmeter device. In other embodiments, the camera is part of a mobiledevice (e.g., a smartphone or tablet device). In some embodiments, theuser is instructed to hold the mobile device with the camera orientedtoward the pattern such that the pattern is viewed through thecorrective lens. An image of the pattern is then captured by the camera.The image may be captured in response to a user indication, such asclicking a physical button or an interface element on the screen of themobile device. In other embodiments, the image may be capturedautomatically once a stable, relatively static image has been obtainedand is in focus, and the lensmeter, corrective lenses, and pattern areappropriately aligned. For example, an accelerometer of the mobiledevice may be used to determine that the camera is relatively still. Ifa focused image can be obtained, the system may attempt to discern thepresence of the pattern within the image using known image processingand detection techniques. In some embodiments, multiple images may becaptured, and an image may be selected for further processing from amongthe multiple images based on such criteria as the image in which thepattern is most in focus, whether the elements are appropriatelyaligned, or the like.

In some embodiments, the object may be an image displayed on a computerdisplay. The object may be a pattern with a known geometry and easilydetectable feature points. According to some embodiments a checkerboardpattern is used.

FIG. 5A illustrates a pattern group 500 in which patterns 510, 520 arepositioned to be used in simultaneously detecting characteristics of twocorrective lenses, such as two eyeglass lenses within an eyeglass frame.The patterns 510, 520 are positioned within a border 530. The border 530includes border reference landmarks 532, 533, 534, 535 at a knownlocations relative to the border 530. The border 530 and/or the borderreference landmarks 532, 533, 534, 535 are used to correct theorientation of the captured image in subsequent steps. In a preferredembodiment, four border reference landmarks are used, though someembodiments may use as few as two border reference landmarks. In oneembodiment, a border reference landmark 532, 533, 534, 535 is located ineach of the four interior corners of the border 530. The borderreference landmarks 532, 533, 534, 535 may be markers recognizable inthe captured image using computer vision techniques, or may be inherentlandmarks detected by computer vision techniques and/or with referenceto the known geometry of the pattern group 500. For example, if it isknown that the border 530 is a rectangle having four interior corners,those four interior corners may be located and used as the borderreference landmarks 532, 533, 534, 535.

The patterns 510, 520 also include a plurality of pattern referencelandmarks 512. The locations of the plurality of pattern referencelandmarks 512 in the captured image are used in subsequent steps todetermine the nature of the distortion introduced by the correctivelens. In some embodiments, a pattern reference landmark 512 is locatedat adjoining corners of squares within a checkerboard pattern. Thepattern reference landmarks 512 may be markers recognizable in thecaptured image using computer vision techniques, or may be landmarksdetected by computer vision techniques and/or with reference to theknown geometry of the pattern group 500.

The locations of the border reference landmarks 532, 533 and the patternreference landmarks 512 are known in the pattern group 500. Those knownlocations allow the pattern group 500 to be used as a reference patterngroup in subsequent steps, against which the locations of those samepoints in captured images may be compared.

In some embodiments, the lensmeter is configured to operate when thecorrective lenses in an eyeglass frame are halfway between the lensmeterand the patterns 510, 520. The patterns 510, 520 are configured andspaced such that each of the patterns 510, 520 is aligned with both thelensmeter and one of the corrective lenses when the corrective lensesare halfway between the lensmeter and the patterns 510, 520. Such anarrangement can be achieved, for example, when the distance between thecenters of the patterns 510, 520 is twice as large as the distancebetween the centers of the corrective lenses. For example, if thedistance between the centers of corrective lenses in an eyeglass frameis 77.5 mm, then the patterns 510, 520 may be spaced such that thedistance between the centers of the patterns 510, 520 is 77.5×2=155 mm.

The patterns 510, 520 and/or the border 530 are sized and configuredsuch that, when the lensmeter captures an image of the patterns throughthe corrective lenses, the openings in a normal-sized eyeglass framewholly surround the patterns in the captured image, meaning the patternsare completely overlaid by the corrective lenses. The openings of theeyeglass frame are in turn wholly contained within the border 530. Thecaptured image can be considered as having one or more first regionscreated from light passing through (i.e., distorted by) the correctivelenses, and one or more second regions created from light passing around(i.e., undistorted by) the corrective lenses.

A captured image 550 illustrating such a configuration can be seen inFIG. 5B. The pattern 510 is wholly contained within an opening 542 of aneyeglass frame 540, and the pattern 520 is wholly contained within anopening 544 of the eyeglass frame 540. The patterns 510, 520 in thecaptured image 550 have been distorted by the corrective lenses in theeyeglass frame 540. The eyeglass frame 540 is wholly contained withinthe border 530. By employing such a configuration, the distortion of thepatterns 510, 520 in the captured image due to the corrective lenses canbe measured, whereas the border reference landmarks 532, 533 remainundistorted.

It will be appreciated that the pattern group 500 illustrated in FIGS.5A and 5B is for illustrative purposes, and different configurations,sizes, or types of patterns and/or borders may be employed, or omittedaltogether, within the scope of the disclosure. In some embodiments,more than one image may be captured, with each image cropped orotherwise limited to contain only one pattern. In other embodiments, oneimage of both patterns is captured, and the image split into two imagesfor parallel processing on each pattern in subsequent steps. In stillother embodiments, video clips of the patterns may be captured, ormultiple static images captured in rapid succession.

It will also be appreciated that lenses having different characteristicswill distort the pattern in the captured image in different ways. Forexample, lenses with positive powers will magnify the pattern in thecaptured image, causing the pattern to appear larger through thecorrective lens. In that situation, the pattern may be sized such thatthe pattern in the captured image is not too large to be fully boundedby the corrective lens. Similarly, lenses with negative powers willdiminish the pattern in the captured image, causing the pattern toappear smaller through the corrective lens. In that situation, thepattern may be sized such that the pattern in the captured image is nottoo small to be identified and processed in identified in later steps.Accordingly, in some embodiments the pattern may be displayed on adisplay device allowing the pattern size to be configured according tothe characteristics of the lens or other considerations. In someembodiments, the user may be provided an interface (either via thedisplay device or the lensmeter 210) to resize the pattern, or to selecta characteristic of the lens and cause a suitably-sized pattern to bedisplayed. In other embodiments, the pattern may be resizedautomatically by the system so that it is the correct size in thecaptured image.

As can be seen in the captured image 550 in FIG. 5B, the border 530 isrotated counter-clockwise from the horizontal rectangular configurationshow in FIG. 5A, and the patterns 510, 520 and border 530 in FIG. 5B aresmaller than their counterparts in FIG. 5A. These variations make itdifficult to directly compare the pattern group 500 of the capturedimage 550 to the reference pattern group 500.

Therefore, returning to FIG. 4, at step 430, the captured image istransformed to an ideal coordinate system. In some embodiments, thecaptured image is transformed to the ideal coordinate system representedby the reference pattern group 500 of FIG. 5A. This transformation mayinvolve rotating, resizing, cropping, and skewing the image to removeany distortions or imprecisions introduced by the image capture process.In some embodiments, the captured image is transformed to an idealcoordinate system by detecting the border reference landmarks 532′,533′, 534′, 535′ in the captured image 550, and transforming thecaptured image 550 using image manipulation techniques to cause theborder reference landmarks 532′, 533′, 534′, 535′ to appear in the samelocation in the captured image as the corresponding border referencelandmark 532, 533, 534, 535 in the reference pattern group 500 of FIG.5A. The border reference landmarks 532′, 533′, 534′, 535′ may bedetected by computer vision techniques, and the border referencelandmarks 532′, 533′, 534′, 535′ or the pixels constituting them may beconfigured to have a shape, color, or other characteristic suitable forperforming such computer vision techniques.

In some embodiments, a matrix transform is determined from the distancebetween the border reference landmarks 532, 533, 534, 535 in thecaptured image 550 and the corresponding border reference landmarks 532,533, 534, 535 in the reference pattern group 500 of FIG. 5A. The matrixtransform is then applied to some or all of the pixels of the capturedimage 550 in order to effect the transformation.

The captured image 550 as it appears after transformation to the idealcoordinate system can be seen in FIG. 5C. The border reference landmarks532′, 533′, 534′, 535′ in this transformed captured image 550 are in thesame location as the border reference landmarks 532, 533, 534, 535 inthe reference pattern group 500 of FIG. 5A.

At step 440, the captured image is processed to determine an overalldistortion from a reference pattern to the pattern of the capturedimage. The overall distortion (i.e., the distortion introduced by thecorrective lens as well as the lens of the camera used to capture theimage) may be determined by comparing the patterns 510, 520 in thecaptured image 550 to the patterns in the reference pattern group 500.In some embodiments, the comparison is performed by comparing theplurality of pattern reference landmarks 512′ in the captured image 550to the plurality of pattern reference landmarks 512 in the referencepattern group 500.

FIG. 6 illustrates the locations of the plurality of pattern referencelandmarks 512′ in an exemplary captured image 550 overlaid over thelocations of the plurality of pattern reference landmarks 512 in thereference pattern group 500. The distance between each pattern referencelandmark 512 a′, 512 b′ in the captured image and its correspondingreference landmark 512 a, 512 b in the reference pattern group may beused to determine a dioptric power matrix P that describes thedistortion (i.e., transformation) from the ideal coordinate system tothe captured image.

Prentice's Rule describes the amount of induced prism in a lens. P canbe used to express Prentice's Rule in matrix form as x_(test)=Px_(ref),where x_(test) is a matrix of the location of the pattern referencelandmark 512 a′, 512 b′ in the captured image, and where x_(ref) is amatrix of the location of the corresponding reference landmark 512 a,512 b in the reference pattern group.

The dioptric power matrix P is given by:

$P = \begin{bmatrix}P_{x} & P_{t} \\P_{t} & P_{y}\end{bmatrix}$ where: P_(x) = S + C sin²θ P_(y) = S+ C cos²θP_(t) = −C sin  θcos θ

Solving algebraically allows for the determination of values for S, avalue related to the spherical power of the lens; C, a value related tothe cylinder power of the lens; and θ, the astigmatism angle of thelens.

The values of S and C describe the distortion introduced into thecaptured image by both the corrective lens and the lens of the camera ofthe lensmeter. Therefore, at step 450, the distortion of the pattern inthe captured image attributable to the corrective lens is determined. Inparticular, the focal lengths of the corrective lens along twoorthogonal axes corresponding to θ and θ+90°, f_(θ) and f_(θ+π°), aredetermined by the following equations:

$f_{\theta} = {\frac{1}{4}\left( \frac{S}{S - 1} \right)}$$f_{\theta + {90{^\circ}}} = {\frac{1}{4}\left( \frac{S + C}{S + C - 1} \right)}$

where l is the distance between the pattern and the lens of the cameraof the lensmeter. To determine the value of l, parameters of the cameraand/or lens may be determined or directly accessed from a data store. Insome embodiments, the focal length f of the camera lens may bedetermined from metadata in the captured image, or in configurationinformation for the lensmeter. The height h of the patterns may beknown. The distance l may be determined from f and other parameters.Methods and systems for determining a distance from an object (e.g., thepattern) are described in U.S. patent application Ser. No. 14/996,917,titled “SMARTPHONE RANGE FINDER” and filed on Jan. 15, 2016, the entiredisclosure of which is hereby incorporated by reference in its entirety.

At step 460, at least one characteristic of the corrective lens isdetermined. In some embodiments, the sphere, cylinder, and axismeasurements of the corrective lens may be determined, allowing for theprescription of the corrective lens to be determined. The spheremeasurement indicates the amount of lens power measured in diopters.Corrective lenses may be prescribed a certain sphere value to correctnearsightedness or farsightedness in all meridians of the eye. In someembodiment, the sphere value may be signed, with a negative valuerepresenting a nearsightedness prescription and a positive valuerepresenting a farsightedness prescription.

The cylinder value indicates the amount of lens power prescribed forastigmatism. The cylinder value may be zero if no correction isprescribed for astigmatism. A cylinder measurement indicates that thecorrective lenses have a first meridian with no added curvature, and asecond meridian, perpendicular to the first meridian, that contains amaximum lens curvature to correct astigmatism.

The axis value described the orientation of the second meridian of thecylinder. The axis value may range from 1 to 180°, with 90°corresponding to the vertical meridian of the eye, and 180°corresponding to the horizontal meridian.

Other values may also be determined for the corrective lenses, such asan ADD value representing an added magnifying power applied to thebottom part of a multifocal (e.g., bifocal or trifocal) lens.

In some embodiments, the sphere, cylinder, and axis measurements of thecorrective lens may be determined by the following equations:

SPH = 1000/f_(θ)${CTL} = {1000\left( {\frac{1}{f_{\theta + {90{^\circ}}}} - \frac{1}{f_{\theta}}} \right)}$AXIS = 180^(∘) − θ

wherein the determination of AXIS is carried out from the perspective ofa wearer of the corrective lens.

The values of SPH, CYL, and AXIS may be displayed on a screen of thelensmeter, may be stored in a memory (e.g., a database, or a file) ofthe lensmeter, and/or may be delivered via the network interface of thelensmeter to another party, such as an eye doctor affiliated with anowner of the corrective lenses, for verification or for filling of theprescription. For example, the processes may be performed by a personwho has eyeglasses but does not know the prescription of those glasses.Information obtained through the methods discussed herein may betransmitted to the person's eyecare professional, who can use theinformation to order a new set of eyeglasses with the properprescription.

The process 400 ends at step 470.

In some embodiments, the requirement that the corrective lenses belocated halfway between the lensmeter and the pattern may be relaxed.The lensmeter and/or the corrective lenses may instead be moved relativeto each other and the pattern, with the lensmeter capturing multipleimages. For each image, values of S and C may be determined as discussedabove. It is known that S and S+C have an extreme value (i.e., a minimumor maximum) when the corrective lenses are positioned halfway betweenthe lensmeter and the pattern. The image for which S and S+C generate anextreme value may be used as the basis for the processes describedherein.

It will also be appreciated that, although the examples given hereinvolve corrective lenses in the form of eyeglasses, the processes andsystems may be applicable to other types of corrective lenses, such ascontact lenses, assuming the contact lenses can be held in a suitableorientation and location for performance of the claimed processes.

In some embodiments, the captured image is not transformed to an idealcoordinate system. Rather, two images are captured: a first image inwhich the corrective lens is disposed between the lensmeter and thepattern, as discussed in various embodiments herein, and a second“reference” image, identical to the first except that the correctivelens has been removed. Because the distortive effect of the lens is notpresent in the second image, the first image may be compared directly tothe second image to determine the amount of distortion using thetechniques discussed with respect to step 440 in process 400.

As discussed above, aspects and functions disclosed herein may beimplemented as hardware or software on one or more of these computersystems. There are many examples of computer systems that are currentlyin use. These examples include, among others, network appliances,personal computers, workstations, mainframes, networked clients,servers, media servers, application servers, database servers and webservers. Other examples of computer systems may include mobile computingdevices, such as cellular phones and personal digital assistants, andnetwork equipment, such as load balancers, routers and switches.Further, aspects may be located on a single computer system or may bedistributed among a plurality of computer systems connected to one ormore communications networks.

For example, various aspects and functions may be distributed among oneor more computer systems configured to provide a service to one or moreclient computers. Additionally, aspects may be performed on aclient-server or multi-tier system that includes components distributedamong one or more server systems that perform various functions.Consequently, examples are not limited to executing on any particularsystem or group of systems. Further, aspects may be implemented insoftware, hardware or firmware, or any combination thereof. Thus,aspects may be implemented within processes, acts, systems, systemelements and components using a variety of hardware and softwareconfigurations, and examples are not limited to any particulardistributed architecture, network, or communication protocol.

As shown in FIG. 3, the lensmeter 210 may be interconnected with, andmay exchange data with, other systems via the network interface 340connected to a network. The network may include any communicationnetwork through which computer systems may exchange data. To exchangedata using the network, the lensmeter 210 and the network may usevarious methods, protocols and standards, including, among others, FibreChannel, Token Ring, Ethernet, Wireless Ethernet, Bluetooth, IP, IPV6,TCP/IP, UDP, DTN, HTTP, FTP, SNMP, SMS, MMS, SS7, JSON, SOAP, CORBA,REST and Web Services. To ensure data transfer is secure, the lensmeter210 may transmit data via the network using a variety of securitymeasures including, for example, TSL, SSL or VPN.

Various aspects and functions may be implemented as specialized hardwareor software executing in one or more computer systems. As illustrated inFIG. 3, the lensmeter 210 includes a camera 310, a processor 320, a userinterface 330, a network interface 340, a memory 350, and lensmetersoftware 360.

The processor 320 may perform a series of instructions that result inmanipulated data. The processor 320 may be a commercially availableprocessor such as an Intel Xeon, Itanium, Core, Celeron, Pentium, AMDOpteron, Sun UltraSPARC, IBM Power5+, or IBM mainframe chip, but may beany type of processor, multiprocessor or controller. The processor 320is connected to other system elements, including memory 350, the camera310, etc.

The memory 350 may be used for storing programs and data duringoperation of the lensmeter 210. Thus, the memory 350 may be a relativelyhigh performance, volatile, random access memory such as a dynamicrandom access memory (DRAM) or static memory (SRAM). However, the memory350 may include any device for storing data, such as a disk drive orother non-volatile storage device. Various examples may organize thememory 350 into particularized and, in some cases, unique structures toperform the functions disclosed herein.

The memory 350 may also include a computer readable and writeablenonvolatile (non-transitory) data storage medium in which instructionsare stored that define a program that may be executed by the processor320. The memory 350 also may include information that is recorded, on orin, the medium, and this information may be processed by the processor320 during execution of the program. More specifically, the informationmay be stored in one or more data structures specifically configured toconserve storage space or increase data exchange performance. Theinstructions may be persistently stored as encoded signals, and theinstructions may cause the processor 320 to perform any of the functionsdescribed herein. The medium may, for example, be optical disk, magneticdisk or flash memory, among others. A variety of components may managedata movement between the storage medium and other memory elements andexamples are not limited to particular data management components.Further, examples are not limited to a particular memory system or datastorage system.

The lensmeter 210 also includes one or more user interfaces 330. Theuser interface 330 may receive input or provide output. Moreparticularly, output devices may render information for externalpresentation. Input devices may accept information from externalsources. Examples of interface devices include keyboards, mouse devices,trackballs, microphones, touch screens, printing devices, displayscreens, speakers, network interface cards, etc.

Although the lensmeter 210 is shown by way of example as one type of acomputer device upon which various aspects and functions may bepracticed, aspects are not limited to being implemented on the lensmeter210 as shown in FIGS. 2 and 3. Various aspects and functions may bepracticed on one or more computers having a different architectures orcomponents than that shown in FIG. 3. For instance, the lensmeter 210may include specially programmed, special-purpose hardware, such as forexample, an application-specific integrated circuit (ASIC) tailored toperform a particular operation disclosed herein. While another examplemay perform the same function using a grid of several general-purposecomputing devices running MAC OS System X with Motorola PowerPCprocessors and several specialized computing devices running proprietaryhardware and operating systems.

The lensmeter 210 may include an operating system that manages at leasta portion of the hardware elements included in the lensmeter 210.Usually, a processor or controller, such as the processor 320, executesan operating system which may be, for example, a Windows-based operatingsystem, such as, Windows NT, Windows 2000 (Windows ME), Windows XP,Windows Vista or Windows 7 operating systems, available from theMicrosoft Corporation, a MAC OS System X operating system available fromApple Computer, one of many Linux-based operating system distributions,for example, the Enterprise Linux operating system available from RedHat Inc., a Solaris operating system available from Sun Microsystems, ora UNIX operating systems available from various sources. Many otheroperating systems may be used, and examples are not limited to anyparticular implementation.

The processor 320 and operating system together define a computerplatform for which application programs in high-level programminglanguages may be written. These component applications may beexecutable, intermediate, bytecode or interpreted code whichcommunicates over a communication network, for example, the Internet,using a communication protocol, for example, TCP/IP. Similarly, aspectsmay be implemented using an object-oriented programming language, suchas .Net, SmallTalk, Java, C++, Ada, or C# (C-Sharp). Otherobject-oriented programming languages may also be used. Alternatively,functional, scripting, or logical programming languages may be used.

Additionally, various aspects and functions may be implemented in anon-programmed environment, for example, documents created in HTML, XMLor other format that, when viewed in a window of a browser program,render aspects of a graphical-user interface or perform other functions.Further, various examples may be implemented as programmed ornon-programmed elements, or any combination thereof. For example, a webpage may be implemented using HTML while a data object called fromwithin the web page may be written in C++. Thus, the examples are notlimited to a specific programming language and any suitable programminglanguage could be used. Thus, functional components disclosed herein mayinclude a wide variety of elements, e.g. executable code, datastructures or objects, configured to perform described functions.

Embodiments described above utilize a process for determiningcharacteristics of a corrective lens using a camera of a mobile device.Other embodiments may be used to determine characteristics of a lens ina number of different applications including: detecting flaws in a lens;comparing characteristics of two different lenses; determining thestructural characteristics of the lens based on the amount ofdiffraction (i.e., distortion) detected; or other applications that callfor determining the characteristics of a lens.

Having thus described several aspects of at least one example, it is tobe appreciated that various alterations, modifications, and improvementswill readily occur to those skilled in the art. For instance, examplesdisclosed herein may also be used in other contexts. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the scope of the examplesdiscussed herein. Accordingly, the foregoing description and drawingsare by way of example only.

What is claimed is: 1-22. (canceled)
 23. A process for determining characteristics of a lens, the process comprising: capturing a first captured image of a pattern through a corrective lens while the corrective lens is at a first distance from the pattern; capturing a second captured image of the pattern through the corrective lens while the corrective lens is at a second distance from the pattern; processing the first captured image to determine a first spherical power measurement; processing the second captured image to determine a second spherical power measurement; selecting, from among a plurality of spherical power measurements comprising the first spherical power measurement and the second spherical power measurement, an extreme spherical power measurement among the plurality of spherical power measurements; and determining, with reference to the extreme spherical power measurement, a lens power of the corrective lens.
 24. The process of claim 23, wherein the extreme spherical power measurement is the largest absolute value among the plurality of spherical power measurements where the corrective lens is a converging lens, and wherein the extreme spherical power measurement is the smallest absolute value among the plurality of spherical power measurements where the corrective lens is a diverging lens.
 25. The process of claim 23, wherein processing the first captured image to determine the first spherical power measurement comprises transforming the first captured image to an ideal coordinate system, and wherein processing the second captured image to determine the second spherical power measurement comprises transforming the second captured image to the ideal coordinate system.
 26. The process of claim 25, wherein transforming the first captured image to the ideal coordinate system comprises: detecting a plurality of captured reference landmarks in the second region of the first captured image; determining a transformation from a plurality of ideal reference landmarks to the plurality of captured reference landmarks; and applying the transformation to the first captured image.
 27. The process of claim 23, wherein processing the first captured image to determine the first spherical power measurement comprises: determining an overall distortion from a reference pattern to the pattern of the first captured image; and determining a distortion of the captured pattern attributable to the corrective lens.
 28. The process of claim 27, wherein the first captured image is captured by a camera having a camera lens, and wherein determining the distortion of the captured pattern attributable to the corrective lens comprises: determining a distance between the camera lens and the pattern; and determining at least one focal length of the corrective lens with reference to the distance and the spherical power measurement.
 29. The process of claim 23, wherein processing the first captured image to determine the first spherical power measurement comprises: detecting, in the first captured image, a plurality of captured pattern landmarks; determining a transformation from a plurality of ideal pattern landmarks to the plurality of captured pattern landmarks; and determining for the corrective lens, from the transformation, the first spherical power measurement.
 30. The process of claim 29, further comprising determining for the corrective lens, from the transformation, a cylinder power measurement and an astigmatism angle measurement.
 31. The process of claim 29, wherein the transformation is a dioptric power matrix.
 32. The process of claim 23, wherein each of the first captured image and the second captured image includes a first region containing the pattern and created by light passing through the corrective lens, and a second region created by light not passing through the corrective lens, wherein determining the distortion of the captured pattern attributable to the corrective lens is performed at least in part with reference to the second region.
 33. The process of claim 32, wherein the pattern comprises a checkerboard pattern, and wherein the second region contains a border.
 34. The process of claim 23, wherein the first captured image and the second captured image are captured by a camera having a camera lens, and wherein the camera lens is positioned at a fixed distance from the pattern during capture of the first captured image and the second captured image.
 35. The process of claim 23, further comprising determining a prescription of the corrective lens, the prescription including at least a sphere value, a cylinder value, and an axis value.
 36. The process of claim 23, further comprising: determining, from the first captured image, a first distance from a camera lens of a lensmeter with which the first captured image was captured to the pattern; identifying a direction to a second location relative to the first location; guiding a user of the lensmeter to the second location; and capturing the second captured image of the pattern through the corrective lens at the second location.
 37. The process of claim 36, further comprising: guiding the user of the lensmeter from the first location to a third location to the second location; and capturing a third captured image of the pattern through the corrective lens at the third location, wherein the third location is substantially halfway between the lensmeter and the pattern.
 38. The process of claim 1, wherein the pattern is a first pattern and the corrective lens is a first corrective lens, and wherein capturing the first captured image further comprises capturing, in the first captured image, a second pattern through a second corrective lens, wherein the first pattern and the second pattern are spaced from each other such that the first pattern and the second pattern are able to be captured in the first captured image when the first corrective lens and the second corrective lens are positioned at a known location relative to the first pattern and second pattern.
 39. A lensmeter comprising: a camera having a camera lens; a visual display; and a processor coupled to the camera, the processor configured to: capture a first captured image of a pattern through a corrective lens while the corrective lens is at a first distance from the pattern; capture a second captured image of the pattern through the corrective lens while the corrective lens is at a second distance from the pattern; process the first captured image to determine a first spherical power measurement; process the second captured image to determine a second spherical power measurement; select, from among a plurality of spherical power measurements comprising the first spherical power measurement and the second spherical power measurement, an extreme spherical power measurement; and determine, with reference to the extreme spherical power measurement, a lens power of the corrective lens.
 40. The lensmeter of claim 39, wherein the extreme spherical power measurement is the largest absolute value among the plurality of spherical power measurements where the corrective lens is a converging lens, and wherein the extreme spherical power measurement is the smallest absolute value among the plurality of spherical power measurements where the corrective lens is a diverging lens.
 41. The lensmeter of claim 39, wherein the captured image includes a first region containing the pattern and created by light passing through the corrective lens, and a second region created by light not passing through the corrective lens.
 42. The lensmeter of claim 39, wherein the processor is further configured to determine the distortion of the captured pattern attributable to the corrective lens by being configured to: determine a distance between the camera lens and the pattern; and determine at least one focal length of the corrective lens with reference to the distance and the spherical power measurement.
 43. The lensmeter of claim 39, wherein the processor is configured to process the first captured image to determine the first spherical power measurement by being configured to: detect, in the first captured image, a plurality of captured pattern landmarks; determine a transformation from a plurality of ideal pattern landmarks to the plurality of captured pattern landmarks; and determine for the corrective lens, from the transformation, the first spherical power measurement.
 44. The lensmeter of claim 43, wherein the processor is further configured to determine for the corrective lens, from the transformation, a cylinder power measurement and an astigmatism angle measurement.
 45. The lensmeter of claim 43, wherein the transformation is a dioptric power matrix.
 46. The lensmeter of claim 39, wherein the processor is further configured to: determine, from the first captured image, a first distance from the camera lens to the pattern; identifying a direction to a second location relative to the first location; guiding a user of the lensmeter to the second location; and capturing the second captured image of the pattern.
 47. A process for determining characteristics of a lens, the process comprising: obtaining a plurality of captured images of a pattern through a corrective lens while the corrective lens is moved relative to the pattern; processing each captured image of the plurality of captured images to determine a plurality of spherical power measurements, each of the plurality of spherical power measurements determined from one of the plurality of captured images; selecting an extreme spherical power measurement of the plurality of spherical power measurements; and determining, with reference to the extreme spherical power measurement, a lens power of the corrective lens.
 48. The process of claim 47, wherein the extreme spherical power measurement is the largest absolute value among the plurality of spherical power measurements where the corrective lens is a converging lens, and wherein the extreme spherical power measurement is the smallest absolute value among the plurality of spherical power measurements where the corrective lens is a diverging lens. 